Multi-channel sound, defined herein as sound reproduced from more than two audio channels, for example, 5.1 or 7.1 channels including 5 or more mid to high frequency channels and a sub-woofer channel is typically reproduced through multiple speakers positioned in front, rear and possibly sides of a listening zone. Multi-channel sound may provide added freedom to recreate an immersive or surround sound listening experience. However, such systems tend to be expensive and complex to install, particularly for smaller installations such as home theatres. Additionally, an acceptable immersive or surround sound listening experience is typically limited to a relatively small listening area located near the centre of the listening zone. Accordingly it would be desirable if a system could be devised that provides fewer loudspeakers yet provides an acceptable surround sound experience for substantially all positions in a listening zone and particularly for multi-channel sound including simulated surround sound.
Various techniques exist to mix multi-channel sound into a two channel format. Some techniques combine all signals into a two-channel format while adjusting only relative gains of the mixed signals. Other techniques include application to an audio signal of frequency shaping, amplitude adjustments and/or phase shifts or a combination of the above during a mixing process. The technique or techniques used may depend on the format and content of the audio signals as well as the intended use of any final two channel mix.
The techniques found in the prior art, including those found in professional recording applications do not provide an effective method for reproducing multi-channel signals in a two channel format that achieves realistic audio reproduction through a limited number of discrete channels. As a result, much ambience information which is responsible for providing an immersive perception of sound may be lost or masked. Despite prior art attempts at reproducing multi-channel sound to achieve a realistic experience in a listening zone through a limited number of channels, there remains much room for improvement.
The present invention may provide a loudspeaker system for reproducing in a listening zone multi-channel sound in a two channel or other limited channel format with an improved sound image, such that substantially all positions throughout the listening zone may perceive sound arriving from each channel with substantially equal arrival times.